I have just planted some Eulalia grass in a bed with some hydrangeas behind them. The idea is that grass will form a boarder. I have planted two gallon grasses about two feet apart. Obviously right now there is a lot of bare space between them.

My question is does the plant base spread itself out as I want thinking to put down some black mulch to help prevent weeds and to make it look ascetically pleasing whilst waiting for the grass to grow in fully. Am I doing more harm than good with the mulch? Am I slowing the growing process down considerably by doing this?

Do you know which Eulalia grass (Miscanthus) you have, and what kind of hydrangea? Yes the grass does spread out, but it also goes high, with some cultivars very high. Depending which Miscanthus and which hydrangea you have, the grass could hide the hydrangeas - perhaps that's your plan in which case ignore the above At two feet apart they should grow together. Mulching them shouldn't be a problem although I have to say I get the impression that some plants don't like the black mulch too much, maybe it gets too hot for them.

So the Eulalia grass is Miscabthus sinensis 'Gracillimus' and the hydrangea is a Smooth Hydrangea (hydrangea arborescena 'Abetwo'). The look we are going for is where the hydrangea comes over the top and the grass folds down to form a soft boarder. I have attached an image.

Ah, right. The numbers the nursery we got them from were slightly different. Hopefully when we cut the grass back each winter it will mean the hydrangea will get tall and bushy and push the grass over.

It will be an experiment I guess!!

Thank you Sue for the quick and helpful responses. I really appreciate it.

On the bright side at least you didn't get one of the tallest Miscanthus What may happen is that the hydrangeas finish blooming before the grass gets tall (Miscanthus are late starters in spring) and then the grass will bloom so you'll have two phases of interest.